High rate transmission systems, such as 40 Gb/s and higher-rate data systems, have large bandwidths requiring a per-channel dispersion compensator. Advantageous in such high rate systems is that these dispersion compensators be tunable. Various types of tunable dispersion compensators (TDCs) have been proposed, including fiber, bulk-optic, and waveguide-based TDCs.
In the case of fiber TDCS, heat-adjustable chirped fiber Bragg gratings have been implemented for their construction. The fiber TDCs have a large tuning range, but each device may be used for only one or two wavelength channels. They also typically cannot be tuned to zero dispersion and also require a relatively long time to tune (i.e., on the order of seconds).
For bulk-optic TDCs, virtually imaged phased array-based TDCs and Gires-Tournois, interferometers have been implemented for their construction. The virtually imaged phased array TDC has a grating-plus-phase-plate arrangement, previously used to shape ultra-short pulses, with a tilted etalon acting as the grating and a curved mirror as the phase plate. The Gires-Tournois-based TDC's, also previously used to shape ultra-short pulses, are multicavity etalons used two or more in series. Both types of bulk TDC's are used for nearly any wavelength channel (known as “colorless” TDCs), however, both types tune very slowly (i.e., on the order of tens of seconds).
For waveguide-based TDC's, ring-resonators and thermo-optic lens waveguide-grating router (WGR) TDCs have been proposed. Unlike bulk-optic solutions, waveguide-based TDCs may be mass produced, automatically and non-hermetically packaged, tuned quickly (milliseconds), and integrated with other functions. The ring resonator TDC is elegant, extremely compact, and colorless, but requires very high index-step waveguides and several electrical controls. The thermo-optic lens-based TDC is colorless, uses low index-step waveguides, and has only one control, but is less compact.